Diagnosing the internal organs of human body by ultrasound is one of the most common modalities used in modern medicine. The ultrasonic waves are non-ionizing and this results in large tolerances as to when ultrasonic waves can be used, e.g., the examination of a fetus. The ultrasonic imaging probes that are particularly dedicated to medical diagnosis can be conveniently divided into two groups: (i) external devices that are used in contact with the skin; and (ii) invasive devices that are employed in circumstances where external scanning results in a lack of precision in the diagnosis or where a higher frequency image is desirable.
In general, external and invasive devices are quite different in terms of design shape and material composition. Indeed, the requirements for the housing materials used in invasive instruments are much stricter than those applied to external instruments. Furthermore, the electrical security of safety level for patients and users must comply with medical regulations for surgical instruments.
The family of invasive ultrasonic imaging probes includes various shapes and designs adapted to fit the internal morphology of the organ to be imaged. A distinction can be made between (i) endocavity probes which are used for endo-vaginal and endo-rectal diagnostics, (ii) endoscopic probes that are elongated versions of invasive instruments wherein the imaging transducer is mounted at the extremity of the (flexible or rigid) tube of an endoscope, which is, in turn, attached to an endoscope handle on which the control functions for the instruments are typically provided, (iii) catheter based probes wherein the ultrasonic transducer is mounted at the extremity or distal end of the corresponding catheter tube, and (iv) special imaging devices designed for specific applications such as brain imaging (e.g., a “Burr Hole” probe) or surgical monitoring (e.g., “Per-Op” probes). Generally speaking, catheter-based instruments for ultrasonic diagnostics are very similar to endoscopic tubes but have a much smaller tube diameter, while Burr Hole type probes are considered to be a customized version of endocavity probe devices. Surgical monitoring (Per-Op) probes are specialized instruments that are specifically designed to fit each particular surgical application. Accordingly, there is a large variety of such instruments, with a small housing being a common characteristic thereof.
Turning first to endoscope-based devices, endoscopic probes are widely used in trans-esophageal echography TEE and intra-vascular imaging (catheter probes). It is evident that the design and shape of diagnostic probes for invasive applications and, more particularly, for endoscopic applications, are governed by the morphology of the organs to be explored; the probes commonly exhibit a long tubular shape to facilitate insertion of the probe into the organ. Generally, the diameter of the tubular portion does not exceed a dozen millimeters (corresponding to the internal diameter of the esophagus).
The above characteristics and features specific to invasive products make them much more expensive and complicated to design and manufacture than conventional diagnosing devices. This is particularly true when the probe is provided with a steering control for the transducer tip during operation (i.e., bending capability) such as is disclosed, for instance, in commonly assigned U.S. Pat. No. 5,681,263 to Flesch. Transducers that are used to equip TEE probes are of high frequency, generally ranging from 5 to 15 MHz. The probe can be provided with a single phased array transducer, dual perpendicular phased array transducers or with a rotated phased array transducer. More recently, some advanced products are based on implementation of a 2D transducer (matrix array).
Similarly to endoscopic ultrasonic devices, ultrasonic probes for endo-rectal and endo-vaginal applications, as well as Burr Hole probes, are built to fit, i.e., to be physically compatible with, the particular organs to be imaged. Generally, such probes are comprised of an external handle and an elongated rigid tube that extends outwardly from the handle and terminates at a transducer tip. The transducer is mounted at the distal extremity of the elongated part of the probe in a manner so as to facilitate accessing of the region of interest. Conventionally, endo-vaginal probes are provided with a curved linear array transducer mounted at the extremity of the tube so as to allow forward scanning of the organ while endo-rectal probes are typically provided with a linear array transducer mounted along with the longitudinal axis of the probe and can be accompanied with a curved array transducer disposed perpendicularly thereto. The frequency of the transducers used in endocavity probes generally ranging from 5 to 10 MHz and the diameter of the inserted part of the probe is typically between 5 and 20 mm.
As indicated above, ultrasonic probes that are designed for use during surgical operations to directly contact human organs are commonly called Per-Op devices. These probes generally comprise an ultrasonic array transducer mounted in a plastic housing that is designed to be sufficiently small and compact so as to be handled by the finger of a surgeon. Several different transducer configurations can be used based on the organ to be imaged and the method of access to the organ that is to be used. Commonly, Per-Op ultrasonic probes are available with the transducer mounted in a probe having a longitudinal, transverse or end-finger configuration. The frequency of the transducer is selected to be suitably high, in a frequency range of about 10 to 20 MHz.
In spite of the use therein of dual transducers, rotating transducers and 2D array transducers, invasive ultrasonic devices still suffer a number of drawbacks and shortcomings with regard to complexity of design, cost of manufacturing and/or lack of reliability. During the past decade, numerous improvements have been made with respect to the basic design of such devices, including, e.g., the provision of rotating phased array transducers, the implementation of 1.5D array transducers for enhancement of the lateral resolution of the images obtained, and the implementation of static 2D transducers as part thereof. The performance and scanning characteristics of such devices have been significantly extended and a corresponding improvement in the resultant diagnostics has resulted. However, the sophistication added to conventional TEE probes has not only enhanced the performance and operating characteristics of the resultant probe but has also raised considerably the manufacturing costs of the probe while simultaneously decreasing the reliability thereof in operation, thereby dramatically increasing the maintenance costs associated with the probe.
It is also noted that endocavity probes that are commonly provided with basic phased array transducers or dual transducer mountings suffer certain limitations in terms of scanning range and the angle of view available during examination. Further, these probes are often used with a biopsy needle for tissue extraction especially in endo-rectal diagnosis, and the accuracy of the placement of biopsy needle is important for the success of the operation. The biopsy needle movement is normally monitored through use of the scanning image, and precise spatial positioning of the needle is desirable to assure that the implicated tissue is sampled. In existing probe devices, a needle guide, which is mechanically secured or fastened to the probe, is provided to enable guiding the needle when the latter is introduced into the tissue. The progression of the needle can observed on the system display unit that provides imaging of the organ, in a scanning plane containing the needle. It will be appreciated that if a misalignment is observed with respect to the biopsy needle, the sampled tissue can be shifted from the theoretical scanning plane without any information being conveyed to the examiner of the organ, i.e., the user of the imaging system. Indeed, as long as the biopsy needle remains within the lateral resolution of the probe, no steering of the needle can be detected by the system.
Currently, TEE probes are generally available with a rotating phased array transducer mounted thereon. The transducer is capable of a rotational movement around the center axis thereof, which is defined as the axis of symmetry of the transducer. This axis also acts as an acoustic energy propagation pathway. Probe devices that include rotating phased array transducers are commonly called “multi plane TEE probes.”
With regard to the endocavity probe devices, a wider variety of probes is available and the design can change with different manufacturers. However, the probes remain quite basic and most improvements involve the use of wide angle array transducers or high density arrays.
The prior art includes two groups of multi-plane ultrasonic probes and both groups include TEE and endo-cavity probes.
The first group of prior art probes is principally comprised of ultrasonic imaging devices including at least two separate transducers which are disposed in the vicinity of each other and which are preferably oriented perpendicularly to each other. These ultrasonic transducers are usually provided in phased-array types that are individually phase shift addressed by the electronics of the associated scanner. In practice, this group of probe devices basically includes endo-cavity instruments and some rare TEE probes. The devices generally incorporate different combinations of transducer mountings. These combinations include, for example, two separate aligned phased arrays disposed perpendicularly each other, a linear array disposed perpendicularly to a curved array, a curved array linearly assembled to a phased array, a phased array geometrically combined with a mechanical sector transducer, and the like. All of the probes belonging to this group are generally considered as standard probe products and are quite widespread throughout the market. However, mechanical sector moving transducer probes are much less common than other the types and the trend is toward electronic scanning devices having a single or dual static transducer array.
The second group of probes is comprised of diagnosing instruments having a dynamic multi plane capability. Such probes are provided with a unique phased array transducer capable of a rotating motion around a vertical axis virtually located at the center of the transducer. The scanning plane of the phased array is, therefore, capable of rotating with a predetermined angle from the initial position thereof. The ability of such arrays to provide rotated scanning planes and to recognize the position of each of the planes, has resulted in an enhanced diagnosis in, for example, cardiology where at least two orthogonal images are often required to achieve the desired diagnosis. This capability is achieved either by providing a single phased array transducer rotatable around its own vertical axis, or by using a matrix (2D) array transducer that is theoretically capable of providing scanning planes of a desired orientation. Such dynamic multi-plane features are chiefly employed in TEE probes and in high-end diagnosing probe devices of the type wherein the significant additional increase in purchase price and in maintenance costs are partially compensated for by the improvement in diagnostic ability and the user-friendly characteristics inherently provided. It is noted that matrix based dynamic multi-plane probes have been recently disclosed as concept or engineering prototypes. A commercial product is not available as yet, so that the focus here will be on rotating phased array based diagnosing probes.
Patents of potential interest here include the following: U.S. Pat. No. 3,881,164 to Kossoff; U.S. Pat. No. 4,640,219 to T'Hoen; U.S. Pat. No. 4,671,293 to Shaulov; U.S. Pat. No. 5,163,129 to Slayton; U.S. Pat. No. 5,681,263 to Flesch, U.S. Pat. No. 5,456,724 to Sliwa; U.S. Pat. No. 5,771,896 to Sliwa; U.S. Pat. No. 6,041,473 to Hossack; U.S. Pat. No. 6,238,336 to Ouchi; U.S. Pat. No. 6,261,234 to Lin; U.S. Pat. No. 6,572,547 to Miller; and EP Patent No. 139,574 to Fornage.
As described above, ultrasonic probes for invasive intervention or diagnostics employ various shapes and configurations with regard to transducer implementation. In European Patent EP No. 139,574 to Fornage et al, there is provided an endocavity ultrasonic probe including at least two imaging transducers employed in a manner such as to provide the user with two tomography scanning images derived from the same region of interest. The ultrasonic transducers are generally of an electronic scanning type but can also be mechanically rotated to form a sector scanning plane. Different transducer implementations are disclosed such as a combination of a linear array and a mechanically rotated transducer, two perpendicularly disposed linear arrays, two curved linear perpendicularly disposed arrays, a linear array and a circular array, and the like. The transducers are disposed on the probe housing in close proximity to produce an intersecting region of the two respective scanning planes.
Similarly, U.S. Pat. No. 6,261,234 to Lin describes a method and apparatus for simultaneously viewing a surgical instrument in two ultrasound imaging planes. The patent also relates to medical endocavity probes wherein a working channel for guiding surgical instruments is provided at the distal tip of the probe. Two separate array transducers are disposed orthogonally in order to provide intersection of the surgical instrument at the intersection of the two scanning planes. The drawbacks of such devices principally concern the crowding or encumbrance of the transducer tip portion produced by mounting several array transducers in close proximity, the complexity of the transducer housing and the complexity or intricacy involved in mounting the assembly onto the probe. Further, the transducers are not located in the same area so that the intersecting zone or region can only be achieved at a certain distance with respect to the emission surfaces of the transducers, thus preventing exploitation of the near field of the image.
In U.S. Pat. No. 6,238,336 to Ouchi, a method is provided which allows the observation of a treatment tool inserted into an ultrasonic imaging instrument. A first curved linear array transducer is provided in the medial area of the transducer tip. This linear array transducer is associated with a sector-shaped mechanically-rotated transducer mounted at the distal portion of the transducer tip. The two transducer images cross perpendicularly so as to enable visualization of the treatment tool being introduced along the azimuth plane of the curved array. The combination of an electronic scanning array and a mechanical sector transducer is very similar to that described in the EP No. 139,574, and the shortcomings and disadvantages described previously are also present.
Other references, such as U.S. Pat. Nos. 5,456,724 and 5,771,896 to Sliwa, Jr. et al., disclose a compact rotationally steerable ultrasound transducer. A circular array transducer is mounted on a circular track and can be rotated by a motor disposed in the vicinity thereof. A position detector is also provided for forwarding transducer position information to the associated imaging system.
Similarly, in U.S. Pat. No. 6,572,547 to Miller et al., there is disclosed a TEE transducer tip including a matrix (2D) array transducer that is capable of rotating or moving the scanning planes on the surface of the transducer.
Both of the Sliwa Jr., et al patents relate to dynamic multi-plane transducer devices, and use a rotating phased array in which implementation of a motorized drive and position encoder are required. The alternate rotation of the transducer during the operation thereof is a source of electrical noise or contact wear. Further, the high degree of integration that the device exhibits results in an increase in cost and a lack of reliability.
With regard to the first Sliwa, Jr. et al. patent (the '724 patent), integration of the 2D array transducer is apparently a more reliable process. However, 2D array transducers provide a scanning image quality that is much lower than that obtained with a 1D phased array, and the complexity involved in addressing all elements of such an array would make the device unattractive for many applications.
In conclusion with respect to these types of prior art transducers, whether incorporated in TEE or endo-cavity probes including intravascular and intracardiac devices, current transducer implementation methods such as aforementioned still impose on manufacturers and users a number of constraints that limit the scanning possibilities of the probes and/or considerably increase the manufacturing cost thereof and, furthermore, reduce the reliability of the resultant probe devices.
One technique that is capable of overcoming all of the aforementioned shortcomings, with an acceptable compromise as to the performance and cost of the resultant device, involves the use of an integrated bi-plane phased array transducer. In this kind of transducer, an ultrasound device is provided wherein a first phased array is provided on a first surface of a piezoelectric member of the transducer, and a second phased array, which is rotated by 90° respect to the first array, is provided on the opposite surface of the same piezoelectric member. Such a transducer has been disclosed in prior art with a number of different variations in the design and construction thereof but the transducer is still difficult to implement in practice and the acoustic performance thereof is limited by the lack of efficient isolation between the first and the second arrays as well as between the elements of the same array.
What may be the first disclosure of ultrasonic transducers having first and second separate arrays disposed in an orthogonal fashion is provided in U.S. Pat. No. 3,881,164 to Kossoff, wherein a main linear transducer array intersects a second transducer array at a middle area thereof, so that a portion of the surface of the second array is lost, i.e., is eliminated. This lost portion corresponds to the width of the first array. However, this early conception cannot be considered to be a true bi-plane construction because the second array of the apparatus is very different from the first array and serves in carrying out Doppler functions or positioning operations.
The first disclosures of the bi-plane transducer concept may have been those contained in U.S. Pat. No. 4,640,291 to T'Hoen and U.S. Pat. No. 4,671,293 to Shaulov, wherein bi-plane composite transducers are described. The piezoelectric member can be provided either without element kerfs, as described in the T'Hoen patent, or with partial grooves formed in the thickness of material, as described in the Shaulov patent. The transducer electrodes are plated on both surfaces of the transducer and correspond, respectively, to first and second transducer arrays. The two arrays are, therefore, provided on the same piezoelectric substrate so that the arrays exhibit very similar characteristics. However, it is noted that no interconnection method is disclosed in these patents and the grooving method described therein limits the cross coupling performance of the transducers.
Another approach to obtaining intersecting scanning planes has been disclosed in U.S. Pat. No. 5,103,129 to Slayton et al. wherein an ultrasonic transducer is provided having an elongated body on which a cross-shaped plate of ceramic is mounted. The ceramic is cross-shaped and the cross arms cross at the center of the ceramic. A number of variations of the crossed configurations are disclosed and these generally include a central area at which the crossing transducer arms intersect. The “hot” or active electrodes of both arrays are all provided on the same face of the piezoelectric substrate so that respective elements of the two arrays cross at the center area of the transducer.
In the Slayton et al patent, the addressing scheme or management approach for the center area is discussed in connection with different embodiments such as a crossed section (meaning that the elements of the two arrays are reduced progressively in elevational width going toward the center of the transducer) or a matrix section (wherein electrode grooves or kerfs are provided on the two arrays without attention to the center area, so that a sub-2D array is thus obtained at this central location). The ground electrode is common to both arrays and is disposed at the front surface of the transducer in contact with an acoustic matching layer.
As a result of constructions described above, the bi-plane transducers as disclosed in the Slayton et al. patent suffer several limitations with respect to their manufacture and operation. In this regard, for the crossed section type, both of the arrays suffer from a substantial diminution of the element surface at the center area of the transducer which results in a dramatic loss of sensitivity at the middle portion of the image (or even the absence of an image at the center of the display). This is unacceptable in diagnostic applications and thus such a transducer construction simply cannot be used in clinical applications. With regard to the matrix section embodiment disclosed in the Slayton et al patent, the transducer can essentially be considered to be a 2D array transducer with complementary prominent transducer arms extending in each cardinal direction. The complexity involved in manufacturing and assembling such a device is greater than that discussed above for standard 2D arrays so that a cost effective implementation of such an array, and the associated addressing electronics, in an invasive medical product is difficult to practically achieve.
In summary, while currently available invasive ultrasound products which still use rotating phased array arrangements or separate phased array assemblies suffer significant disadvantages, a bi-plane approach has not been viable for important applications because of difficulties associated with making bi-plane transducers as well as the lack of a viable technical solution with respect to the problem of integrating such a bi-plane transducer into an invasive probe. Consequently, there exists a need in the art for a bi-plane transducer capable of providing comparable performance to a conventional phased array and for an invasive probe that incorporates such a bi-plane transducer therein in a manner so as to provide high quality medical diagnosis.